This invention is related to co-pending application Ser. No. 151,033, filed on Feb. 1, 1988 now U.S. Pat. No. 4,730,805.
Power supplies for use with electronic equipment, such as computers, are frequently designed for use with either 110 volts or 220 volts A.C. The output of such supplies is generally a D.C. voltage which must be maintained at a substantially constant value regardless of the A.C. input voltage.
In order to satisfy this requirement, some means is normally provided to sense the level of the A.C. input and then modify the power supply circuitry to provide a single level D.C. output. A commonly used technique is to switch the circuit configuration from a full wave rectifier to a voltage doubler. The switching is achieved either manually or automatically.
Many of the prior art systems operate with the possibility that the circuitry will not be in the correct mode when the A.C. voltage is applied. Whether this is due to an incorrect manual setting or an incorrect automatic setting created by an interruption, default or spike in the A.C. input voltage, such incorrect settings can be harmful to the electronic equipment. This is particularly true when the A.C. input voltage is high but is erroneously detected as being low because the D.C. output voltage can exceed a safe level. The reverse problem, i.e., erroneously detecting low A.C. input voltages as being high, can produce too low a D.C. output, also creating problems which effect equipment performance.